DODGE SENSORS
This advice is based on my experience with one 1994 Grand Caravan with 3.3L gasoline fuelled engine meeting US federal emission standards.
I presume you have a service manual, though I may include brief pointers from it to make this advice more cohesive. Some of what I cover here is in the service manual if you can find it, often not in the section you'd expect it in.
Also read my wiring diagram errors page
And beware of odd terminology:
- "dash panel" apparently means the forward side of the firewall, not the instrument panel.
- my left and right directions are from the driver's view.
- pinouts in Chrysler's wiring diagrams appear to be looking at the harness side of connectors
The wiring manual shows harness routing, component location, and splice locations.
To save you the chase-around time and correction of errors in Chrysler’s diagram, and provide conceptual understanding of system function, I provide the following information on wiring of sensors:
Most sensors are wired as though they are a potentiometer, though most actually contain electronic circuits: reference power, ground, and a signal value that varies between the ground and reference power.
Use only a high impedance meter to test sensors and the PCM.
Chrysler helpfully used the ECM contact number for the wire number, so for example wire K4 eventually connects to ECM contact number 4. (The second and subsequent instances splices add a suffix to the wire number (so for example wire K4 has splices K4, K4-1, etc). Additional names near splices seem to refer to physically location not function.)
Most sensors have a signal ground reference wire going to the ECM, usually contact 4, via shared wire/splices K4.
Most sensors have a reference power input from the ECM, shared with some other sensors:
- for MAP and TPS that is 5vdc from contact 6, shared wire K6.
- for cam and crank position that is 8 or 9vdc from contact 7, shared wire K7.
Each sensor has a signal wire going to the ECM, typically a voltage between the power and ground wires that varies with value of what is being sensed.
- MAP goes to contact 1
- TPS goes to contact 22
- crankshaft goes to contact 24
- camshaft goes to contact 44
The coolant temperature sensor for the ECM does not need a reference voltage, only a signal wire to contact 2 and a shared ground reference wire K4, it is typically a temperature-sensitive resistor.
(The coolant sensor for the gages has only a single wire to the gage, ground return is via the engine block, it is typically a temperature-sensitive resistor.)
The oxygen sensor has a signal reference wire (K4) shared with other sensors, heater power from the fuel pump relay (wire A141), basic shared ground (K1) for the heater, and signal wire A41 to ECM contact 41.
The gasoline fuel tank gage sender shares a basic ground with the pump motor and has a wire going to the gage, it appears to be a simple potentiometer giving a resistance value to the gage.
Most of the sensors are well identified in the factory service manual, but a few are hard to find:
- you should be able to get at the connector for the crankshaft sensor from above, perhaps by removing the throttle body (it is below the inlet, lying across the transmission housing - the connector is remote from the sensor). Otherwise you’ll need to work from below. If you have long arms you can reach the connector pair to get it apart and apply contact cleaner, while lying on your back under the raised vehicle. Better to get it on a high hoist. The harness runs forward then outboard to join a larger harness below and behind the battery.
- the park/neutral switch (fwd left corner bottom) and transmission range switch (inbd of it) can easily be reached from under the front of the vehicle
- the output speed sensor (above park/neutral switch on fwd-facing transmission structure) can be reached from above inside the engine compartment, long arms help. Perhaps from below as well.
-the camshaft sensor is hidden in the right end of the engine, inboard of the aft diagonal brace to the engine mount, aft of the thermostat housing but lower. The too-short pigtail on mine was routed forward, its white connector mated with a black harness connector, then the harness routed over the pair and into a collector harness assembly that runs across the engine to the left end. The pigtail is covered with black corrugated plastic loom that should be replaced, perhaps with woven loom pushed against/over the sensor.
It’s attaching bolt is just below the bottom flange of the alternator bracket, the sensor is forward of that pointing down.
Removing the brace should be a 10 minute job, but due to http://www.allpar.com/forums/topic/146850-results-of-chrysler%e2%80%99s-bad-design-94-caravan-33l-installation/ it is more like 40 minutes. 15 mm socket for the forward bolt, 18mm socket for the mount bolt nut (my standard one was long enough to reach over the end of the bolt that sticks out, but short enough so the ½" ratchet could go between PS reservoir and ignition cables to get more throw), 18mm something to hold the bolt head.
Moving the ignition PS reservoir might help general arm access (unfasten and hang over by the spring tower), removing the serpentine belt will help as the sensor bolt is inboard of it.
I think there is room to remove the sensor and install a new sensor, apparently the only alignment needed is proximity to the sprocket which apparently is provided by the paper spacer that should come with a new sensor. (Push the sensor in until it stops, the clamp has a slotted attach hole, the sprocket will rub the paper off into the oiling system?). Expect to need a medium or long extension, ¼" ratchet should suffice, socket may be 8mm.
You do want to avoid coolant leaks else antifreeze may drain or spray onto the sensor wires and connector pair.
Harness routing varies. Some is:
- TPS and IACV run to the aft left corner of the engine, then forward, then outboard into large connectors below and aft of the battery.
- a harness runs across the engine to the left aft corner , then outboard into large connectors below and aft of the battery. It collects ignition coil, camshaft, MAP, and oxygen sensor wiring.
- there's a harness running across the front of the engine at the bottom.
Sensors and much other wiring go to the left front fender, as the Power Distribution Center and PCM are there.
- do make sure connectors are latched, the good seal requires pushing the halves together firmly, Chrysler's design has little over-travel.
Diagnosis is not as simple as you might expect:
- fault codes are not specific enough in some cases, but do hint to an area of item.
- fault codes are not necessarily logged for intermittent conditions (they may not be until a number of repeats in a certain period of time).
- false fault codes can occur in unusual circumstances. (I've seen IACV and TPS, for example, during start attempts when the problem was a disconnected camshaft sensor. When cleared by the procedure to clear Adaptive Learn values they did not recur.)
- I experienced lack of a code when a camshaft sensor connector became disconnected.
The factory service manual provides some information on what is not monitored when, but is inadequate. (For example:
- oxygen sensor not monitored until engine warm, as it is not used until then because it has to be hot to work.
- fewer sensors are used during starting (I suspect more are used when the engine starts to run than during cranking, but was puzzled by the lack of camshaft sensor fault code as the PCM requires usable signal from both cam and crank sensors. Perhaps because the design uses both to get cylinder identification and piston position in the cycle in order to time ignition and injection, but does not time injection during cranking, I was semi-consciously thinking the PCM would try to prevent valve-piston collision if the cam drive had broken but actually it is too late by then.)
Questions/corrections welcomed.
© Keith Sketchley Page version 2016.05.23
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